BRITISH FLIES 45 



CERA (up to the end of the Asilida?) the anal cell is very distinct and long, 

 but when the Microphona are reached the anal cell becomes very short, 

 and (with the exception of some Hyholinm, which thereby naturally form 

 the first snbfamily of the JSm2ndcc) the lower branch of the postical vein 

 bends down so abruptly or even recurrently as to close the anal cell quite 

 close to the base of the wing (or the anal cell disappears altogether), and 

 this continues through the Atiiericera with a few exceptions; some of 

 these exceptions liowever occur where they would be least expected, such 

 as amongst the Tri/prJidce or Ortalidce. The discalcell is present in almost 

 all the Brachycera until after the Asilidrr, so that with the curtailment 

 of the anal cell the discal cell also becomes at first uncertain and then 

 disappears; in many families the npper branch of the fork of the postical 

 vein is connected with the discal cell by the small cross-vein, but some- 

 times this small cross-vein is al)sent and the upper branch of the postical 

 fork then forms for a greater or less distance the lower margin of the 

 discal cell, or sometimes {Scenoijinidm) almost the whole lower margin; 

 in the Empidm the discal cell often disappears and even when present has 

 almost all its lower margin formed by the npper branch of the postical 

 vein, and in the succeeding families of the Brachycera the discal cell 

 entirely disappears, but reappears again in a different form in the SyrpUdm 

 and other families of the Athericera. The closed fourth posterior cell 

 (or its equivalent) becomes a strong feature in the Acantliomeridce, 

 Mydaida:, A2nocerida\ and Asilida:, l)ut is rare in other families, though it 

 occasionally crops up as in Xylomyia, Lam^rromyia, etc. 



The antenna gradually change from a flagellum composed of 

 nnmerous joints in the Nemocera, in which the joints range from being 

 extremely individualised in the Cecidomyidcr, to the more solid annulated 

 flagellum of Bihionidcc or the remarkable pectination of Ctenophora, to a 

 more solid joint in the Brachycep.a, in which however the earlier families 

 retain an obvious similar annnlation, and even in the remarkable genus 

 liJutrhicerus imitate the pectination; this annnlation of the flagellum 

 becomes less and less distinct, and at the next stage {Tahanidm) the first 

 annnlation grows much larger than the others and reduces these others 

 into a sort "of style, and thenceforward the style becomes more and 

 more solid though still with indication of joints, and often ends in a thin 

 hair, until in passing to the next stage the third joint of the antenna3 

 becomes a solid round, ovate, conical, reniform, or elongate joint, and 

 usually has a thin more or less hair-like apical arista ; m ^ome Leptida', 

 etc., this arista may appear to be placed rather dorsally in consequence 

 of the peculiar shape of the third joint, but it is not until the Dolicliopodidm 

 are reached that the arista becomes decidedly dorsal, and then when the 

 Brachycera are passed it becomes normally dorsal and only exceptionally 

 apical. The absolute absence of any style or arista in the ligulate 

 antenna of Scenopinus, and the remarkable club-like style of Mydaidw, 

 oucrht to crive somo clue to the relationship of the Dermatina. The 



